Mapping Dark Matter’s Invisible Super-Clumps

One of the coolest things about astronomy is its ability to handle unknowns. Invisible things. The places where on old maps, people would have simply said Here There Be Dragons.

Researchers using the Hubble Space Telescope are studying the Abell 901/902 galaxy supercluster – a 2.6 billion light-years distant region of space holding hundreds of often violently interacting galaxies – to try to understand the structure of matter underlying it.

Now they say they’ve successfully mapped the clumpy distribution of dark matter across the huge space, helping to explain how this mysterious, invisible substance is affecting

Just as a reminder, dark matter is a still-theoretical substance that scientists believe makes up a majority of the universe’s actual mass, yet is invisible and undetectable to our ordinary instruments. Mapping it is thus a little on the shall-we-say tricky side.

But this team of researchers, led by Meghan Gray of the University of
Nottingham in the United Kingdom and Catherine Heymans of the
University of British Columbia in Vancouver, is using a clever method to get around the whole invisible problem

They’ve turned their attention to the galaxies behind the supercluster, looking at how the light produced by these more-distant stars is bent as it travels through Abell 901/902. The cluster’s galaxies themselves produce their own space-bending gravitational field, but can’t account for the entire warping of the light’s path.

The remainder is the influence of the dark matter. Using this technique, they’ve found that the invisible substance appears to be gathered irregularly into massive, dense clumps, totaling close to 100 trillion times the mass of our Sun.

"Thanks to Hubble’s Advanced Camera for Surveys, we are detecting for the first time the irregular clumps of dark matter in this supercluster," Heymans said. "We can even see an extension of the dark matter toward a very hot group of galaxies that are emitting X-rays as they fall into the densest cluster core."

The team is also learning much about the the violent life cycle of the individual galaxies in the cluster, which collide, strip gas away from each other, and distort as they move through the gravitational fields of the dark matter clusters, the team said.

The findings are being presented today at the American Astronomical
Society in Austin, Texas, and will be published in the Monthly Notices of the Royal Astronomical Society.

(Image: The distribution of dark matter in supercluster Abell 901/902.
The purplish spots represent the map of dark matter created with
Hubble observations, superimposed on a visible light image taken with the MPG/ESO 2.2-meter telescope in La Silla, Chile.

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